How To Characterize Multimodal Samples Using Particle Characterization Equipment

A common customer request in the field of particle characterization is to characterize samples `containing multiple size distributions mixed together in a single sample. This type of test provides an excellent demonstration of an instrument’s resolving power and accuracy. However, the results expected from such a test depend upon a variety of factors such as the core technology, product design, sample preparation, and percentage difference in size of the underlying samples. While many experimenters may focus on testing two pure samples consecutively (eg, running 50 and 100 nm in two separate consecutive tests), it is much more difficult to test samples that are mixed together (eg, mixing 50 and 100 nm beads and resolving the peaks simultaneously).

This is a subtle, yet important distinction for customers. Most real world samples do not resemble the pure, monomodal polymer beads that are frequently used to test instrument performance. Rather, they are mixture of various sizes and components—and are not necessarily easy to separate into constituents. Therefore, it is most useful from an applications perspective if an instrument can resolve multiple component peaks from a single mixed sample.

This application note will discuss the topic of size resolution in particle characterization and advantages and disadvantages of various techniques. Several demonstrations of complex, mixed samples in various instruments are provided. Readers will benefit from a deeper understanding of what to expect from a given product based on its technical underpinnings.